Morphometric x-ray absorptiometry (MXA)

ABSTRACT

MXA Scan analysis in accordance with an exemplary embodiment of the invention can be viewed as a process of placing points on the lateral morphometry image at the anterior, mid, and posterior positions of the inferior and superior endpoints for each vertebral body in the spinal region of interest. These point locations are then used to calculate the anterior, mid, and posterior heights of the vertebral bodies. These heights are then compared to one another and to known normal values for the heights and ratios of the heights for each vertebral body and among vertebral bodies to quantify the degree of vertebral deformity.

This is a continuation of application Ser. No. 08/176,418 filed Jan. 3,1994. Now U.S. Pat. No. 5,483,960.

REFERENCE TO MICROFICHE APPENDIX

The present application incorporates a microfiche appendix with twosheets of of microfiche having 153 frames (see parent U.S. Pat. No.5,483,960).

BACKGROUND OF THE INVENTION

The invention is in the field of imaging using penetrating radiation andpertains in particular to obtaining and processing penetrating radiationmeasurements and especially to morphometric x-ray absorptiometryreferred to by the acronym MXA.

In fields such as the diagnosis of osteoporosis, it can be desirable toconfirm a fracture associated with low bone material density, such as ahip, wrist or vertebral fracture. For example, see Seeley D. G., BrownerW. S., Nevitt M. C., Genant H. K., Scott J. C., Cummings S. R.: Whichfractures are osteoporotic? Third International Symposium onOsteoporosis, Copenhagen, Denmark; Osteopress ApS, Copenhagen, 1990;Vol. 2, pp 463-464. Lateral thoratic and lumbar spine films have beenutilized for the diagnosis of vertebral fractures in order to confirmcrush and wedge deformities of vertebral bodies in the rangeencompassing T4 and L4 vertebrae. A number of studies have evaluatedmethods for the identification of vertebral fractures by vertebralmorphometry and the correlation thereof with readings of radiologists.For example, see A) Hedlund L. R., Gallagher J. C.: Vertebralmorphometry in diagnosis of spinal fractures, Bone Miner 1988; 5: 59-67,B) Hedlund L. R., Gallagher J. C., Meeger C., Calcif Tissue Int 1989;44: 168-172, c) Davies K. M., Recker R. R., Heaney R. P.: Normalvertibral dimensions and normal variation in serial measurements ofvertabras, J Bone Min Res 1998; 4: 341-349 D) Smith-Bindman R., SteigerP., Cummings S. R., Genant H. K.: The index of Radiographic Area (IRA):a new approach to estimating the severity of vertebral deformity. BoneMiner 1991; 15;137-150. E) Smith-Bindman R., Cummings S. R., Steiger P.,Genant H. K.: A comparison of morphometric definitions of vertebralfracture, J Bone Min Res 1991; 6: 25-34, F) Minne H. W., Leidig G.,Wuster C. H. R., et al: A newly developed spine deformity index (SDI) toquantitate vertebral crush fractures in patients with cateoporosis, BoneMineral 1988; 3: 335-349, G) Sauer P., Leidig G., Minne H. W., DuckeckG., Schwarz W., Siromachkostov L., Ziegler R.: spine deformity index(SDI) versus other objective procedures of vertebral fractureidentification in patients with osteoporosis: a comparative study, JBone Min Res 1991; 6(3): 227-338, H) Eastell R., Cedel S. L., WahnerN.W., Riggs B. L., Melton L. H.: Classification of vertebral fractures.J Bone Min Res 1991; 6(3): 207-215. Stoner S: Change in vertebral shapein spinal osteoporosis, Some vertebral morphometry techniques involvedigitizing conventional radiograms (x-ray films) and obtaining anterior,posterior and mid-vertebral heights. However, there can be disadvantagesin this approach such as operator imprecision in placing the points fordigitization on the radiograms, the use of multiple exposures to imageboth thoracic and lumbar regions of the spine due to the relativelylarge attenuation difference between the thoracic and lumbar areas, thepossible need for retakes, and the radiation dose that can be associatedwith this procedure (such as 900 mRem without repeat exposures). Inaddition, geometric distortion can be a factor in using such digitizedconventional x-ray films because they typically are obtained using conebeam geometry. As a result of such geometric distortion, differentpoints in the radiogram are magnified and distorted in relative positionin different ways. For example, areas closer to the edge of the filmimage are magnified more and are viewed at a somewhat oblique angle,whereas areas close to the center are magnified less and are viewed atan angle closer to perpendicular. Still in addition, the identificationof vertebral levels can be difficult and film handling and archiving caninvolve considerable overhead. Rectilinear scanning, using a bonedensitometer with a thin pencil beam of x-rays can counter the geometricdistortion problem but can introduce the disadvantage of a much longerscanning time to acquire the necessary x-ray data. The use of a fan beamCT scanner in a scout view mode can decrease the scanning time ascompared with rectilinear scanning. See W. A. Kalender, et al.,Determination of Geometric Parameters and Osteoporosis Indices forLumbar Vertebrae from Lateral QCT Localizer Radiographs, 8thInternational Workshop on Bone Densitometry, Bad Reichenhall, Germany,Apr. 28-May 2, 1991. However, it is believed that the proposed CT imageswere not dual energy images and that the proposal may not completelyaddress the issues of geometric distortions and/or vertebralmagnification factor differences as between the AP and lateral images.Moreover, it is believed that QCT (quantitative computerized tomography)so used in morphometry typically images a relatively limited region ofthe spine such as the T12 through L4 vertebrae.

When bone densitometry equipment is used to obtain penetrating radiationimages useful in morphometry, typically a patient is placed on a tableand remains stationary while a radiation source moves relative to thepatient position. A radiation detector is positioned on the oppositeside of the table from the source to detect radiation transmittedthrough the patient. The radiation source and detector are usuallymechanically linked by a structure such as a C-arm to ensure alignmentbetween them. Both x-ray tubes and isotopes have been used as a sourceof the radiation. In each case, the radiation from the source iscollimated to a specific beam shape prior to reaching the patient tothereby restrict the radiation field to the predetermined region of thepatient opposite which are located the detectors. In the case of usingx-rays, various beam shapes have been used in practice or proposed,including fan beam, pencil beam and cone or pyramid beam shapes.

Bone densitometry systems are manufactured by the assignee hereof undertradenames including QDR 2000plus, QDR-2000, QDR-1500, QDR-1000plus,QDR-1000W and QDR-1000. Certain information respecting such equipmentcan be found in brochures originating with the assignee hereof andidentified by the designators B-108 (September 1993 ) USA, B-109(September 1993 ) USA, S-117 (September 1993 ) USA and S-118 (October1993 ) USA. Commonly owned U.S. Patents pertaining to such systemsinclude U.S. Pat. Nos. 4,811,373, 4,947,414, 4,953,189, 5,040,199,5,044,002; 5,054,048, 5,067,144, 5,070,519, 5,132,995 and 5,148,455 aswell as U.S. Pat. Nos. 4,986,273 and 5,165,410 (assigned on its face toMedical & Scientific Enterprises, Inc. but now commonly owned). Commonlyowned U.S. Patents application Ser. No. 08/156,287 filed on Nov. 22,1993 also pertains to a bone densitometer. Said Patents and applicationand said brochures are hereby incorporated by reference herein. Otherbone densitometry systems are believed to be offered by other companies,such as the Lunar Corporation of Madison, Wis. See, e.g., J. Hanson, etal., New Imaging Bone Densitometer, Presented at: The American Societyfor Bone and Mineral Research 15th Annual Meeting, 18-22 Sep. 1993,Tampa, Fla., USA, an undated flier entitled Product Information EXPERT,and U.S. Pat. No. 5,228,068, none of which is necessarily admitted to beprior art against the invention claimed in herein. Note the discussionof an approach to morphometry in said U.S. Pat. No. 5,228,068.

For a general background concerning MXA, see Morphometric X-RayAbsorptiometry (MXA), a document prepared by the assignee hereof andidentified by the designation W-126 (October 1993 ) USA, which is herebyincorporated by reference. Other articles of interest include A)Cummings S R, Black D M, Nevitt M C, Browner W S, Cauley J A, Genant HK, Mascioli S R, Scott J C, Seeley D G, Steiger P, Vogt T M:Appendicular bone density and age predict hip fracture in women, JAMA1990; 263(5): 665-668, B) Kleerekoper M, Parfitt A M, Ellis B I:Measurement of vertebral fracture rates in osteoporosis. Osteoporosis:Procedings of the Copenhagen Symposium on Osteoporosis Jun. 3-8, 1984.Christiansen, Arnaud, Nordin and et al. ed. 1994 Department of ClinicalChemistry, Glostrup Hospital. Denmark, C) Leidig G, Storm T, Genant HK,Minne HW, Sauer P, Duckeck G, Siromachkostov L, Sorensen CH, Ziegler R:Comparison of two methods to assess vertebral fractures. Third IntSymposium on Osteoporosis, Copenhagen, Denmark; Osteopress ApS,Copenhagen, Denmark, 1991; Vol 2, pp 626-628, D0 Ettinger B, Black DM,Nevitt MC, Rundle AC, Cauley JA, Cummings SR, Genant HK: Contribution ofvertebral deformities to chronic back pain and disability, J Bone MinerRes 1992; 7(4): 449-456.

Summary of the Invention

A vertebral morphometry process in accordance with a non-limitingexample of the invention estimates vertebral body dimensional parametersto quantify vertebral deformities. For a morphometry examination inaccordance with the invention, typically two scans are performed such asan AP centerline scan to determine spine alignment and a lateralmorphometry scan for morphometric analysis. The centerline scan is an APscan similar to that acquired in AP/Lateral scanning; however, whereas atypical centerline scan used for bone densitometry purposes may image aspinal region that is about 6 inches long, a typical centerline AP scanfor morphometry in accordance with the invention can image a spinalregion which in the range of 20 inches long. Similarly, the secondmorphometry scan, e.g., a lateral scan which images a spinal regionwhich also can be in the range of about 20 inches in length. Both scanscan include all thoracic and lumbar vertebrae, or a subset thereof suchas thoracic vertebrae T4-T12 and lumbar vertebrae L1-L4.

Morphometry scans are analyzed in accordance with an example of theinvention by defining the positions of three reference points, anterior,posterior, and mid, on each of the two endplates, superior and inferior,of each vertebral body. For a baseline morphometry scan, the centerlineand morphometry scans are displayed side-by-side. The system can suggestpoint placements based upon its pre-stored knowledge of normal vertebralanatomy. Each vertebral body is described by its own coordinate systemdetermined by the inferior anterior point of each vertebra and by ahigh-degree polynomial, such as a fourth degree polynomial, made to fitthrough those points. This is designed to reduce operator-inducedvariation and to accelerate image evaluation. An operator can change thesuggested point positions by adjusting the positions on each displayedvertebral body of three markers on each endplate in ascending order. Asecond position cursor automatically tracks the position of the activereference point on the AP centerline scan. For each vertebral bodyanalyzed, a Vertebral Dimensions Report can be created to provideestimates for: (a) posterior height, which is the distance between theposterior points on the superior and inferior endplates of the specificvertebral body; (b) mid height, which is the distance between the midpoints on the superior and inferior endplates of the specific vertebralbody; (c) anterior height, which is the distance between the anteriorpoints on the superior and inferior endplates of that specific vertebralbody; (d) wedge parameter, which is the ratio of the anterior height tothe posterior height of that specific vertebral body; and (e) mwedgeparameter, which is the ratio of the mid height to the posterior heightof that specific vertebral body. In addition, during analysis of afollow-up morphometric scan using a "compare" feature, the follow-upmorphometry scan can be displayed beside the baseline morphometry scanimage. The vertebral endplate markers from the baseline scan analysiscan transfer automatically onto the follow-up scan and move as a groupto help position the markers as a group on the morphometry scan. Then,individual markers can be adjusted if necessary.

In broader terms, the invention is embodied in a method and a systemwhich image a patient with dual energy penetrating radiation to obtainpaired vertebral AP and lateral scan images and utilize the pairedimages to carry out computer-assisted vertebral morphometric analysis.In the course of the lateral scan, a constant vertebral magnificationfactor is maintained despite the fact that the vertebral centerlineprojection on a horizontal plane may curve or skew. In addition, thesame vertebral magnification factor can be maintained for each of the APand lateral scans. Still in addition, the same magnification factor canbe maintained as between an initial examination and a later, follow upexamination of the same patient. Stated differently, in accordance withone aspect of the invention a constant vertebral magnification factorcan be maintained for all examinations of all patients, as well aswithin each examination, in order to ensure better fit of examinationresults to each other and to a knowledge database. Such constantvertebral magnification factor can be achieved by maintaining a constantdistance between the source of the penetrating radiation and a vertebralcenterline. The AP scan can be taken within a relatively short timeinterval, such as less than a minute (e.g., 25 seconds) while thelateral scan can take much longer, such as more than a minute (e.g., 10minutes). If the AP scan will be used for bone mineral density analysisin addition to its use for morphometry in accordance with the invention,the AP scan also can take several minutes, e.g., 6 minutes. For thelateral scan, the fan beam of penetrating radiation can maintain anorientation in which one of the boundaries of the fan is substantiallyhorizontal (and parallel to the patient bed surface). In addition to theparameters referred to above, the morphometry according to the inventioncan derive estimates of Kyphosis, Lordosis and Scoliosis parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be obtained from thefollowing description when taken in conjunction with the drawings, inwhich:

FIGS. 1A and 1B illustrate a side-by-side display of paired lateral andAP vertebral images obtained and displayed in accordance with anembodiment of the invention for use in computer-assisted vertebralmorphometry in accordance with the invention.

FIG. 1C illustrates a local coordinate system used for each vertebra inaccordance with an embodiment of the invention.

FIG. 2 illustrates a patient positioned for centerline AP/morphometryscans.

FIGS. 3A and 3B illustrate a display of an enlarged lateral image and acorresponding AP image, respectively.

FIG. 4 illustrates the orientation of a fan beam of x-rays for a lateralscan.

FIG. 5 illustrates a procedure for placing markers on a lateralvertebral image.

FIGS. 6A and 6B illustrate an enlarged lateral image and an AP image,respectively, with corresponding synchronized markers or cursorsthereon.

FIG. 7 illustrates a vertebral dimensions report.

FIG. 8 illustrates morphometry summary analysis report.

FIG. 9 illustrates a vertebral deformity report.

FIG. 10 illustrates a spinal deformity report.

FIGS. 11A and FIG. 11B illustrates analysis of a follow-up morphometryscan.

FIG. 12 is a perspective view illustrating an alternative bonedensitometry system useful in practicing the invention.

FIG. 13 is a sectional view illustrating the system of FIG. 12 when usedfor an AP scan.

FIG. 14 is a sectional view similar to that of FIG. 13 but illustratingthe system when used for a lateral scan.

FIG. 15 is a block diagram illustrating functional components of asystem useful in carrying out an embodiment of the invention.

FIG. 16 illustrates the measurement of a Kyphosis factor.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIGS. 1A and 1B illustrate a side-by-side display of a spinal lateralimage on the left and a spinal AP image on the right, respectively,obtained with the previously identified QDR-2000 series bonedensitometry system available from the common assignee. For morphometrypurposes, the operation of the commercially available system is modifiedunder the control of morphometry software operating in accordance withthe invention, in conjunction with the commercially available controlsoftware for the systems installed in this country, which is herebyincorporated by reference. The morphometry software is provided as amicrofiche appendix.

To obtain paired AP and lateral images of the type illustrated in FIG.1A and FIG. 1B the bone densitometry system first carries out an APscan, modified in accordance with the invention to cover a longer regionof the spine, to obtain the AP image shown in FIG. 1B. This image isobtained by scanning a supine patient, for example a patient in theposition illustrated in FIG. 2, with a fan beam of x-rays oriented suchthat the central axis of the x-ray beam is vertical. A procedure forobtaining the paired scans and processing them is described in pagesG1-34 of the QDR-2000 Operator's manual and User's Guide supplied byHologic, Inc. of Waltham, Mass., Document No. 080-0384 Revision E, whichpages are herby incorporated by reference. In the example illustrated inFIG. 2, the x-ray source is below the patient and the x-ray detectorsare above the patient, and the patient is centered on a table such thatthe vertebral column centerline substantially coincides with the centralaxis of the fan beam. The resulting image is still called an AP(anterior-posterior) image in this specification, although in thisconfiguration it can be called more accurately a PA (posterior-anterior)image. For the purposes of this invention, no distinction is madebetween AP and PA images. Unless the AP image is to be used for otherpurposes, such as for bone mineral density analysis, it can be takenrelatively quickly, such as over a time of less than a minute (e.g., 25seconds). The image resolution therefore can be lower, but sufficientfor morphometry purposes in accordance with the invention, and theoverall examination time and patient dose can be thus reduced. Thesystem generates the AP image and carries out image processing whichincludes an identification of a vertebral centerline and a startposition and a region of interest for the morphometry scan. A C-armwhich supports the x-ray source and detector is then pivoted while thepatient remains in the supine position such that, as illustrated in FIG.4, x-ray source 10 is at one side of patient 12 while x-ray detector 14is at the other side, and such that one boundary of fan-shaped x-raybeam 16 is horizontal and parallel to the top surface of patient table18. The line connecting the lowermost detector element in x-ray detector14 and the origin of beam 16 is just above table 18, e.g., 1/8" to 1/4"above the table. In this manner, geometric distortion can be suppressedand the measured x-ray beam need not pass through table 18. The systemthen carries out a lateral scan in which the distance between the originof beam 16 and the vertebral centerline is the same as for the AP scanand, moreover, remains the same during the lateral scan even if theprojection of the centerline on a horizontal plane deviates (withinlimits) from a straight line or from a line perpendicular to the planedefined by the origin of beam 16 and detector elements in x-ray detector14. To maintain the distance between the beam origin and the vertebralcenterline constant, the source-detector assembly can move along thesource-detector axis during the lateral scan, as controlled by thesoftware controlling the morphometry scan in accordance with theinvention, depending on the position of the vertebral centerlineidentified as a result of the AP scan. After the lateral scan image isavailable, and is displayed alongside the AP image as illustrated inFIG. 1A and FIG. 1B, markers are placed on the endplates of eachvertebral body, for example in the spinal region including vertebraeT4-L4, on three reference points (anterior, posterior, and mid) on eachof the two endplates (inferior and superior) of each vertebrae. Thepreferred procedure for placing markers is: placement of InferiorAnterior Points; adjustment of Inferior Posterior Points; adjustment ofSuperior Anterior Point for L4; adjustment of Point Positions Relativeto Fit; and adjustment of Point Positions Relative to Image. At eachphase in this procedure, the system suggests point placements based uponits knowledge of normal vertebral anatomy. Each vertebral body isdescribed by its own coordinate system determined by the inferioranterior point of each vertebra, and a fourth degree polynomial fitthrough those points is made. This is designed to reduceoperator-induced variation and to accelerate image evaluation. A dualwindowing feature in the system allows the operator to scroll the (thelateral image) in FIG. 1A up or down while the right image (the AP)remains fixed and shows the entire spinal region which was imaged in theAP scan. Such scrolling is illustrated in FIG. 3A and FIG. 3B. If whileplacing markers the operator moves a marker off the screen (up or down),the system can automatically scroll the display to show that portion ofthe spine. In a preferred embodiment of the invention, an active markeris displayed as a blue circle on the image in FIG. 1A. The position, onthe spine, of the active marker is denoted on the image in FIG. 1B by ablue dashed line which moves along the AP image in synchronism with anymovement of the marker on the image in FIG. 1B, in order to ensure thatthe markers on the two images shown in FIG. 1A and FIG. 1B,respectively, track each other in position at all times. Markers areplaced sequentially, as indicated in FIG. 5, beginning with the anteriormarker on the inferior endplate of the lowest vertebra of interest, inthis case L4. The operator observes the markings which are alreadyplaced on the image (lateral) in FIG. 1A by the system derived from on aknowledge database of typical vertebral anatomy. The operator moves thefirst marker, using arrow keys or a mouse that can be provided as a partof a commercial QDR-2000 system, so that the marker is located as closeto the inferior endplate, and as far to the anterior, as possiblewithout going outside of the vertebral body. After the first marker ispositioned correctly, the operator presses an <Insert> key, in responseto which the system stores information defining the position andidentity of the point. The system automatically changes the activemarker to the next vertebral body, which the operator similarlypositions and enters. The system and the operator continue up the spineuntil all markers for anterior point positions, on the inferiorendplate, are complete. The system provides the location of the activepoint (vertebral body level) and the active marker number. This isdisplayed under the morphometry image at the far right as illustrated inFIG. 1A and FIG. 1B (See also FIG. 6A and FIG. 6B). The first twocharacters provide the location on the spine (specific vertebral body),and the last number indicates the active marker. A similar procedureadjusts the inferior posterior point positions. Points are adjustedbeginning with the posterior marker on the inferior endplate of L4 inthis example. Similarly, the superior anterior point positions areadjusted. A group of points can be moved with respect to the curve ofthe spine. When the points are positioned correctly, a report can begenerated. Morphometry scan results can be reported by different methodsillustrated in FIGS. 7, 8, 9 and 10. A Vertebral Dimensions Report (FIG.7) shows the vertebral dimensions in millimeters (mm). Anterior (AH),mid- (MH) and posterior (PH) vertebral heights are listed.Anterior/posterior height ratios (WEDGE) and mid/posterior (MWEDGE)height ratios are also provided. A Morphometry Summary Analysis Report(FIG. 8) shows the calculations (only) from each of the other reportscreens. Since all of the calculations appear on one page, this reportcan provide a convenient presentation of the information. A VertebralDeformity Report (FIG. 9) labels vertebral deformities according to analgorithm proposed, e.g., by McCloskey et al. (McCloskey E. V., SpectorT. D., Eyres K. S., O'Rourke N., Fern D. E., Kanis J. A. 1993 Assessmentof vertebral deformity--validation of a new method with highspecificity. Osteoporosis Int 3(3): 138-147). Anterior, central,posterior and crush deformities are evaluated separately. The number ofdeformities is totaled per vertebra and per deformity type. A SpinalDeformity Index Report shows the Spine Deformity Index (SDI) asproposed, e.g., by Minne et al. (Minne H. W., Leidig G., Wuster C. H.R., et al., 1988 A newly developed spine deformity index (SDI) toquantify vertebral crush fractures in patients with osteoporosis. BoneMineral 3: 335-349). A number greater than 0 indicates a deformity,while a no entry indicates that a vertebra is not consideredsignificantly deformed. Indices are listed separately for anterior (Ha),mid (Hm) and posterior (Hp) vertebral heights. The indices are totaledper vertebra and per deformity type. In accordance with another featureof the invention, a Compare procedure can be used on follow-up scans tooptimize marker placements from one scan to another, and to save time.Since marker positions, on a new scan of the same patient, are likely tobe very close to the prior scan, time can be save qd by automaticallymatching-up the markers in accordance with the invention. The Compareprocedure comprises: Scan selection; Image adjustment; Marker placement;and Report generation. The Scan Selection step is the selection of abaseline scan for the comparison. The Image Adjustment step comprisesadjusting the contrast and brightness of the displayed image, ifnecessary, to give the best definition to the vertebral endplates. Inthe Marker Placement step, the current (follow-up) morphometry scanappears on the left of the screen as illustrated in FIG. 11A and thebaseline scan appears on the right, as illustrated in FIG. 11B. Thesystem transfers the marker positions from the baseline to the follow-upmorphometry scan. The operator can adjust the points on the image (thelateral image) in FIG. 11A as a group to allow compensation for changesin spinal curvature that may have occurred between the two scans due topositioning changes or due to changes in patient anatomy. If the shapeof the vertebral bodies has changed, it may be easier to repositionmarkers using the "Adjust Positions Relative to Image" capability of thesystem after having used the "Adjust Positions Relative to Fit"capability.

Stated in more formal terms, MXA Scan analysis in accordance with anexemplary embodiment of the invention can be viewed as a process ofplacing points on the lateral morphometry image at the anterior, mid,and posterior positions of the inferior and superior endpoints for eachvertebral body in the spinal region of interest. These point locationsare then used to calculate the anterior, mid, and posterior heights ofthe vertebral bodies. These heights are then compared to one another andto known normal values for the heights and ratios of the heights foreach vertebral body and among vertebral bodies to quantify the degree ofvertebral deformity.

MXA Scan analysis in accordance with the invention can follow analgorithm which is a knowledge based and semi-automatic procedure forplacing the required points. For baseline scans (no previous analyzedscan for the patient), the algorithm can use prior knowledge ofrelationships between vertebral heights based on published literatureand on analysis of morphometric measurements previously carried out inaccordance with the invention for other patients and selected inaccordance with objective and/or subjective criteria for inclusion inthe knowledge database. As information is supplied for a given patient,the algorithm incorporates that information to adjust the proposedplacement of the points. For FollowUp scans, the previous scan resultsare used as the initial guess for the placement of points and modifiedto compensate for changes in patient positioning and/or possibledeformity of the vertebral bodies. Points are placed either by moving acursor via directional commands entered on the computer keyboard or bymanipulation of the positions via a pointing device such as a mouse. Thealgorithm is substantially the same regardless of which implementationis used, except as noted below.

The following steps are followed for Baseline Scans in accordance with anon-limiting example of the invention. Note that an example of thesoftware controlling the process is set forth in the microficheappendix:

1. An operator of the system places (preferably with a mouse) one pointper vertebra starting at L4 and extending 1 vertebra beyond the topmostvertebra to be quantified. The points should follow the outline ofanterior edges and should be placed at the inferior anterior edge of theendplates. This generates a set of I anterior points A₁ -A_(I), whereA_(i) is defined by coordinates (X_(ai) , Y_(ai)). If the mouse is notbeing used, then the algorithm guesses at the point position for thenext vertebra based on the position(s) of the points on the inferiorvertebrae.

2. A 4th degree polynomial is fit through A₁ -A_(I) :

    x=a.sub.a y+b.sub.a y.sup.2 +c.sub.a y.sup.3 +d.sub.a y.sup.4 +e.sub.a (1 )

Note that x (posterior/anterior axis) is fit as a function of y (caudalto cranial axis).

3. For each vertebral body, a local coordinate system is defined withthe inferior anterior point of the vertebral body as the origin and theperpendicular to the fit as the local y axis, as illustrated in FIG. 1C:

4. The process generates a set of inferior posterior points for thespecified vertebral bodies. The points are initially positioned relativeto the respective local coordinate system for each vertebral body at adistance from the inferior anterior point proportional to the distancebetween the inferior posterior point and inferior anterior point on thelowest vertebral body. The ratio of these distances can be maintained inthe knowledge base which guides the process. The operator then adjuststhe positions of the inferior posterior points for the respectivevertebrae. As a point is adjusted, similar adjustments are madeautomatically to inferior posterior points on superior vertebral bodiespreserving the angle between local y axis and a line connecting theinferior posterior and anterior points and the ratio of the distancesbetween the inferior posterior and anterior points.

5. The process generates a single superior posterior point at apredefined distance along the 4th order fit. The operator then adjuststhe location of this point.

6. The process then generates the remaining points as follows:

a) Superior anterior points are generated along the fit at distancesproportional to the distance between the inferior anterior and superioranterior points on the lowest vertebral body. The ratio of thesedistances is maintained in the knowledge base which guides the process.

b) Superior posterior points are generated similarly as if the anteriorfit passed through the inferior posterior point. For the lowest vertebra(usually but not necessarily L4), the posterior height is calculated asa fixed proportion of the anterior height. For the remaining vertebrae,superior posterior points are then generated at distances proportionalto the distance between the inferior posterior and superior posteriorpoints on the lowest vertebral body. The ratios of these distances aremaintained in the knowledge base which guides the process.

c) Superior and Inferior midpoints are then generated. A point (l) iscalculated midway between the inferior posterior and anterior points. Asecond point (u) is calculated midway between the superior posterior andanterior points. The inferior and superior midpoints are then locatedalong a line connecting l and u such that the distance between theinferior and superior midpoints corresponds to data in the knowledgebase. The inferior and superior midpoints are offset equally from thepoints (l) and (u).

7. The operator then adjusts the points as described below. Pointpositions are stored at grid locations where the grid spacing is afunction of the data acquisition. All distances are expressed inmillimeters.

To adjust point positions after the points are placed as discussedabove, the process supplies three (3) modes of adjustment:

1) Selected points (relative to fit). The subset of points which can bemoved is a function of the currently selected cursor. Point motion isperformed relative to the fourth order polynomial fit in the localcoordinate system of each vertebral body as defined above. The possiblemotions are summarized below for the different candidate cursorpositions:

a) Cursor at inferior anterior point. The fit is recalculated as theinferior anterior point is moved. The positions of all points on allvertebrae relative to their local coordinate system are preserved.

b) Cursor at inferior posterior point. The angle and distance of theinferior mid and superior anterior points are adjusted corresponding tochanges in the angle and distance of the inferior posterior pointrelative to a coordinate system centered at the inferior anterior point.The angle and distance of the superior posterior and superior mid pointsare adjusted relative by a similar amount by relative to the newposition of the superior anterior point (e.g., if the angle of theinferior posterior point changes 10 degrees relative to the inferioranterior point, then the angle of the superior posterior point changes10 degrees relative to the angle between the old superior posterior andsuperior anterior points but calculated from the new superior anteriorpoint position).

c) Cursor at inferior mid point. The superior mid point is adjustedrelative to the current superior anterior point proportional to thechange in the position of the inferior midpoint relative to the inferioranterior point.

d) Cursor at superior posterior point. The superior mid point isadjusted relative to the current superior anterior point proportional tothe change in the position of the superior posterior point relative tothe superior anterior point e) Cursor at superior anterior point. Thesuperior mid and superior posterior points are adjusted relative to theinferior anterior point proportional to the change in the position ofthe superior anterior point relative to the inferior anterior point.

f) Cursor at superior mid point. Only the superior mid point is moved.In each case, point positions in vertebral bodies superior to thecurrent vertebral body are also adjusted. Motion is limited so that nopoint can be moved outside the image frame.

2) Individual point. Only the specified point is moved. The point to bemoved is indicated by color and a cursor. The point position may bechanged via the keyboard or the mouse.

3) All points (relative to image). All the points may be moved. All thepoints are marked in a color to indicate that they are moveable. Aspecific point is indicated as a cursor although all the points move asa group. Point positions may be changed via the keyboard or the mouse.Motion is the same for all points. Motion is limited such that no pointcan be moved outside the image frame.

In baseline scans, the operator first performs type 1 adjustments andthen proceeds to move individual points, if necessary, using type 2adjustments. Type 3 adjustments are intended for Follow-Up scans tocompensate for overall shifts in general position positioning.

In the case of follow-up scans, where morphometry in acccordance withthe invention has been carried out for the patient on a previousoccasion to obtain a Baseline Scan, a Follow-Up Scan procedure isfollowed:

1. Baseline and follow-up scans are presented side-by-side. The pointpositions from the previous (baseline) scan are reproduced on thefollow-up scan. The operator initially performs a type 3 repositioning(all points relative to image) to compensate for any overall shift inpatient positioning (or initial scan starting position)

2. The operator then selects type 1 repositioning (relative to fit) andadjusts the point positions to reflect differences in the curvature ofthe spine. For the most part, the operator will need to select andadjust specific inferior anterior positions to reproduce the coordinatesystem for each vertebral body. In the case of incident deformity, theoperator should also adjust the endplates by moving the inferior andsuperior posterior point positions and possibly even correct the midpoint placement (if necessary).

3. If necessary, the operator can reposition individual points usingtype 1 repositioning.

The results of the procedures described above can be used to calculateand assess a number of additional parameters characterizing a patient.For example, a Kyphosis index can be calculated in accordance with theinvention as illustrated in FIG. 16, by measuring the distance (l)between the lower anterior point on T4 and the intersection of thespinal centerline with a straight line from that point on T4 and thecorresponding point on L4, measuring the distance (h) from that line tothe thoracic curve, and multiplying the ratio (h/l) by the factor 100.

While the description above refers to using a QDR-2000 system to obtainthe AP and lateral images, in the alternative the system described insaid commonly owned patent application and illustrated in FIGS. 12, 13and 14 can be used. As illustrated in FIGS. 12-14, a patient 1 lieshorizontally (in a supine position) during scanning on a table 2. X-rayradiation produced by an x-ray source 3 located beneath table 2 istransmitted through patient 1 to a detector 4 having an array ofdetector positions and located above patient 1. Both x-ray source 3 anddetector 4 are supported on a rigid arm 5 which maintains a selectedsource-to-detector distance and alignment. In this example of theinvention, x-ray source 3 has a stationary anode. Adjacent x-ray source3 is a slit collimator 6 made of a material an x-ray opaque materialsuch as lead or tungsten of sufficient thickness to substantially blockx-rays from source 3. One or more selectable slits have been machinedinto collimator 6 to allow passage of the x-rays there-through. Thepreferred embodiment includes a 1 mm wide collimator slit. The x-rayradiation from the x-ray source 3 passes through the slit in thecollimator 6 and forms a fan shaped beam of x-rays 3a. The anglesubtended by beam 3a and the distance between its origin at the focalspot of the x-ray tube and patient 1 are selected such that beam 3awould not cover the entire cross-section of a typical adult patient atany one time but would cover only a selected portion of the width. Inthe preferred embodiment, fan beam 3a has a maximum fan angle of 22degrees. Of course, x-ray beam 3a not only has width (along the X-axisillustrated in the Figures) but also has a thickness along the Y-axisthat is defined by the width of the slit in collimator 6 and itsdistance from the origin of beam 3a. A scan line is defined by the areaof the patient irradiated at any one time, i.e. the width and thicknessof the x-ray beam over which data is collected at one point in time. Acomplete pass or scan consists of a set of adjacent scan lines obtainedover a period of time such that the entire region of interest has beenmeasured.

Opposite x-ray source 3 is detector 4 which in this embodiment comprisesapproximately 200 detector elements arranged in a linear configurationalong the XZ plane which is about 16" long and is about 42" from theorigin of beam 3a (42" source-to-detector spacing) and subtends a 22degree fan angle. The detector elements making up detector 4 are fixedwith respect to x-ray source 3. However, both x-ray source 3 anddetector 4 can move with respect to patient 1 and table 2. One motiontranslates fan beam 3a along the patient axis defined by the spine,i.e., in the Y-direction. Another motion rotates beam 3a around thepatient. The center of rotation is at a point C determined by thesupport arm 5 and the method of rotation employed. In this embodiment,the detectors and x-ray source are mounted to C-arm 5 which rotates on aset of rollers 7. Thus, the center of rotation is determined by theouter radius R of the C-arm, and is not at the origin (focal spot) ofbeam 3a.

Table 2 can move horizontally along the X-axis as well as verticallyalong the Z-axis. These motions can be carried out by using atoothed-belt driven by a stepping motor or a DC servo motor, althoughother implementations such as stepper-motor driven lead-screws can alsobe employed. To perform a scan, a series of scan lines of data must beacquired. To do this, C-arm 5 carrying the x-ray source 3 and detector 4is moved along the Y-axis along the length of patient 1. This motionmoves detector 4 and x-ray source 3 to form a succession of spatiallyoverlapping scan lines adding up to a scanned rectangular area. Thesignals produced by the detectors in response to x-rays impingingthereon at successive scan lines are digitized by an analog to digital(A/D) converter and are stored, for example on disk. A computerprocesses the signals from the A/D converter into densityrepresentations and images using the principles disclosed in the priorart discussed in the background section of this disclosure.

For body structures of interest such as the spine, only a single pass offan beam 3a along the Y-axis is required because typically the area ofinterest in the patient's body is covered by fan beam 3a as shown inFIGS. 13 and 14 for the Posteroanterior (PA) spine. However, in order toreduce geometric distortion and improve registration between lateral andPA views, in accordance with the invention the system maintains asubstantially constant distance between x-ray source 3 and a centerlineof the spine of patient 1. To achieve this, a series of movements ofC-arm 5 and table 2 are required to ensure that the table and C-armclear each other and to ensure that the requisite source-spine distanceis maintained. In this embodiment, table 2 is moved along the X-axis andthe Z-axis appropriately while C-arm 5 is rotated about an Y-axispassing through point C until the desired lateral position is reached.

FIG. 15 illustrates an embodiment in accordance with the invention inblock diagram form. Gantry 10 includes the structure illustrated inFIGS. 12-14 as well as a suitable power supply for the x-ray tube andthe motors needed to move table 2 and C-arm 5 and to operate collimator6 in a manner similar to that in said QDR-2000 system. Detector 4supplies x-ray measurements to A/D convertor and preliminary processor12 which carries out processing similar to that carried out in saidQDR-2000 system. The output of element 12 is supplied to a processor 14which performs various calculations and forms an image in a mannersimilar to that used in said QDR-2000 system and, additionally, carriesout morphometric calculations. Data and images from processor 14 aresupplied to a console 16, display 18 and a recording device 20 forpurposes and in a manner similar to those in said QDR-2000 system.Two-way arrows connect the elements of FIG. 15 to illustrate the factthat two-way communication can take place therebetween. Conventionalelements have been omitted from the Figures and from this descriptionfor the sake of conciseness.

For example, the illustrated equipment can be used as a first step toderive a PA view of the patient's spine. The view can be in the form ofa processed image in digital form, or it can be in the form of hard copyon x-ray film or on some other medium. The PA spine image is analyzed todetermine the center of the vertebral column, and this information isused to maintain during a lateral scan the same distance between thesource and the spine centerline as during the PA scan. For example, theeach of the PA and lateral scans can cover entire T4 to L4 range in asingle scan at a source to detector distance of 40 inches.

When both a PA view and a lateral view are available, selected points onthe vertebrae images can be marked, for example as discussed in thearticles by Smith-Bindman et al. discussed in the Background of theInvention. For example, each vertebral body is outlined by six pointswhich can serve as the basis of the calculation of posterior, mid- andanterior heights.

While a preferred embodiment of the invention has been described indetail, it should be understood that changes and variations will beapparent to those skilled in the art which are within the scope of theinvention recited in the appended claims.

We claim:
 1. A method for vertebral morphometry comprising the stepsof:obtaining paired AP (anterior/posterior or posterior/anterior)centerline and lateral morphometry images of a patient covering at leastthe T4 (thoracic 4 ) through L4 (lumbar 4 ) vertebrae by using radiationto carry out an AP scan and a lateral scan without moving the patientbetween the scans, wherein said AP scan is carried out first to producean AP image which is analyzed to determine the centerline of thepatient's vertebral column and said centerline is used to maintain aconstant distance between the centerline and an origin of the radiationwhile carrying out the lateral scan; displaying the paired AP image andthe lateral image side-by-side together with a pair of spatiallysynchronized cursors pointing to anatomically corresponding currentlocations on both images to help identify vertebrae and visualizespatial relationships of anatomy and pathology between said AP andlateral images which are displayed side-by-side; designating six pointsfor each vertebra with said cursor; calculating posterior, mid- andanterior vertebral heights and vertebral wedge indices with the use ofpoints designated in the designating step; and displaying calculatedheights and indices characterizing the patient.
 2. A method forvertebral morphometry as in claim 1, wherein the radiation comprises afan beam and in which the step of obtaining said images comprisesmaintaining during said lateral scan an orientation of the fan beam inwhich one of the boundaries of the fan beam is horizontal.
 3. A methodfor vertebral morphetry comprising the steps of:imaging a patient toobtain paired vertebral AP (anterior/posterior or posterior/anterior)and lateral scans, at least one of said AP and lateral scans beingobtained by imaging the patient with penetrating radiation energy; andutilizing said paired scans to carry out computer-assisted vertebralmorphometric analysis comprising manual designation by an operator ofthe locations of at least a plurality of morphometrically significantpoints on a lateral image resulting from said lateral scan.
 4. Amorphometric method comprising the steps of:imaging a patient to obtainpaired AP (anterior/posterior or posterior/anterior) and lateral scanimages, at least one of said paired images being obtained withpenetrating radiation energy; and utilizing said paired images todetermine a curve connecting anterior points of the lateral vertebralimage and to derive a Kyphosis index related to the ratio of a deviationof the thoracic curve from a line connecting the lower anterior point ofvertebrae T4 (thoracic 4 ) and L4 (lumbar 4 ) and the distance from thelower anterior point of vertebra T4 and the intersection of the curvewith a polynomial fit.
 5. A system for vertebral morphometrycomprising:a bone densitometer imaging a patient to obtain paired AP(anterior/posterior or posterior/anterior) and lateral scan vertebralimages, at least one of the paired images being obtained withpenetrating radiation energy; a display for side-by-side display of saidimages showing spatially synchronized movable cursors pointing at alltimes at anatomically corresponding portions of the AP and lateralimages to help identify vertebrae and to help visualize spatialrelationships of anatomy and pathology between said AP and lateralimages which are displayed side-by-side; and a processor coupled withthe display and responsive to the designation of points on the lateralimage, including the manual designation and/or confirmation of points byan operator, to carry out vertebral morphometric analysis.
 6. Avertebral morphometry method comprising the steps of:imaging a patientwith penetrating radiation to obtain paired vertebral AP(anterior/posterior or posterior/anterior) and lateral scan images;displaying said images side-by-side together with a pair of spatiallysynchronized cursors pointing to respective spatially correspondingpoints on said AP and lateral images to help identify vertebrae andvisualize said spatial relationships of anatomy and pathology betweensaid AP and lateral images which are displayed side-by-side; utilizingthe displayed images and said synchronized cursors to carry outcomputer-assisted vertebral morphometric analysis by placing markers onpredetermined points on said displayed images to mark predeterminedpoints on one or more of the vertebral, wherein the markers areinitially placed by computer-assisted suggestion based on knowledge ofvertebral anatomy.
 7. A vertebral morphometry method as recited in claim6, wherein each vertebral body forming the vertebrae is described by itsown coordinate system.
 8. A vertebral morphometry method as recited inclaim 7, wherein each coordinate system is determined by a predeterminedpoint of each vertebra.
 9. A vertebral morphometry method as recited inclaim 8, wherein each predetermined point is the inferior anterior pointof each vertebra.
 10. A vertebral morphometry method as recited in claim9, wherein a polynomial fit is made through each predetermined point.11. A vertebral morphometry method as recited in claim 10, wherein thepolynomial fit is a fourth degree polynomial fit.
 12. A vertebralmorphometry method as recited in claim 6, wherein one of the imagesdisplayed side-by-side can be scrolled while the other image remainsfixed.
 13. A vertebral morphometry method as recited in claim 6, whereinthe computer-assisted suggestions for marker placement are based onknowledge of normal vertebral anatomy.
 14. A vertebral morphometrymethod as recited in claim 6, wherein the computer-assisted suggestionsfor marker placement are based on prior knowledge of vertebral anatomyof the same patient.
 15. A vertebral morphometry method as recited inclaim 6, further comprising a step of determining heights of varioussections of each vertebral body using the placed markers.